I have a Galaxy S3 that has been locked by the Android device manager

It has been locked my Android device manager and switches to a screen that says call owner to an old number of ours that no longer works we can't remember the password or code can anybody please help us unlock it

Welcome to Android Central! How did you forget your password or PIN--is this a really old phone that you haven't used in a while? If you fail the unlock enough times, does it ask for your Google account information and password?